A difficulty in targeting triple-negative (TN) breast cancer is that neoadjuvant therapies are not very effective. Therefore, it is important to identify new potential targets for this subtype of breast cancer. Protein Kinase D3 (PKD3) in TN breast cancer cells regulates proliferation, invasion and multidrug resistance. This predicts that targeting PKD3 with a chemical inhibitor either alone, or in combination with current chemotherapy could be a successful strategy to target this subtype of breast cancer. It is our hypothesis that triple negative breast cancers underwent an isoform switch from expression of PKD1 to expression of PKD3. We further hypothesize that PKD3 drives the oncogenic phenotype of these cancers and that a pan PKD inhibitor will be effective for treatment alone or in combination with currently-used therapeutics. To test this we will: Examine if triple-negative Breast Cancers show an isoform switch in PKD expression to the oncogenic subtype PKD3 (Specific Aim 1); evaluate combinations of CRT0066101 with standard cytotoxic chemotherapy in triple-negative breast cancer cells (Specific Aim 2); and target PKD3 in triple negative cancers and evaluate effects on primary tumor growth and metastasis (Specific Aim 3). Successful completion of our project will identify PKD3 as new molecular target for triple-negative cancers. This is important since this subtype of breast cancer is aggressive and difficult to treat. Overall our results will provide the basis for the development of novel and more potent therapeutic strategies for patients with triple-negative Breast Cancer.